Laser-marked polymer workpiece

ABSTRACT

A laser-marked polymer workpiece is described. The workpiece has a transparent component and an opaque component applied to at least one region of the transparent component. A mark is introduced onto a surface of the opaque component facing the transparent component with at least one laser. The mark is introduced, via a laser, through the transparent component. The mark is a lightening of the surface of the opaque component on which the mark was introduced.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of U.S. patent application Ser.No. 14/351,437 entitled “Laser-Marked Polymer Workpiece” filed on Apr.11, 2014, which is the U.S. national stage of International PatentApplication PCT/EP2012/069994 filed on Oct. 10, 2012 which, in turn,claims priority to European Patent Application EP 11189471.3 filed onNov. 17, 2011, all three of which are incorporated herein by referencein their entirety.

BACKGROUND OF THE INVENTION

The invention relates to a laser-marked polymer workpiece, a method forits production, and its use.

Plastic panes for motor vehicles are typically produced in themulti-component injection molding method. Customarily, a darkly colored,usually black, opaque component is applied to a transparent component inthe edge region of such a pane. In the region of the opaque component,the pane can be bonded, for example, glued, to the motor vehicle body ina manner not visible to the observer.

By means of a mark or inscription, for example, a manufacturer's code,approval mark, a production date, or optical effects can be applied tothe pane. Different methods are known for marking plastic panes. Withinjection molding of the pane, the mark can be introduced as a negativeor positive relief in the surface of the pane. However, image sharpness,contrast, minimum font size, and level of detail are limited. Inaddition, because of the relief, marginal coating distribution problemscan occur at the time of lacquer coating of the pane.

Alternatively, a mark can be engraved or milled into the pane as arelief after injection molding. Here, as well, at the time of lacquercoating of the pane after marking, coating distribution problems canoccur. Application of the relief after lacquer coating of the panedamages the lacquer layer.

Methods for laser marking of plastic panes are also known. In that case,the marking is based on a darkening of a region of the surface of thepane as a result of laser irradiation. Here, the mark is also notprotected against mechanical and chemical damage as well as UVradiation. With lacquer coating of the pane after laser marking, coatingdistribution problems can occur. Application of the mark after lacquercoating of the pane damages the lacquer layer. The darkening can beproduced by other known methods even in the interior of a plastic pane.Since the darkened mark is not discernible against the background of theopaque component in the edge region of the pane, the mark must beapplied in the transparent visual field of the pane, where it can have adisturbing effect.

Methods, with which a laser mark can be introduced into polymerworkpieces in the form of a darkening, are, for example, known fromDE19944372A1, WO2010019194A1, DE19732306A1, and WO2010054077A2.

Also known are methods of laser marking in which laser sensitivematerials specially introduced into the workpiece are used, for example,from DE102009028937A1 and WO2010023102A1. However, the production of theworkpieces is rendered more difficult by the necessity of the lasersensitive materials.

SUMMARY OF THE INVENTION

The object of the present invention is to make available a markedpolymer workpiece as well as a method for its production, wherein thedisadvantages of the prior art are avoided.

The object of the present invention is accomplished according to theinvention by a laser-marked polymer workpiece according to the claimedsubject matter.

The laser-marked polymer workpiece according to the invention comprisesat least the following characteristics:

a transparent component and

an opaque component applied to at least one region of the transparentcomponent,

wherein a mark is introduced with at least one laser through thetransparent component into the surface of the opaque component facingthe transparent component.

The advantage of the laser-marked polymer workpiece resides in thepositioning of the mark in the interior of the polymer workpiece. Thus,the mark is protected against mechanical and chemical damages and otherenvironmental influences. In addition, the mark does not result incoating distribution problems when the polymer workpiece is covered by acoating after marking. In addition, the mark is arranged in the regionof the opaque component of the polymer workpiece. If the polymerworkpiece according to the invention is, for example, the pane of amotor vehicle, the transparent visual field is not negatively impactedby the mark.

The object of the present invention is further accomplished according tothe invention by a method for producing a laser-marked polymerworkpiece, wherein:

a) a transparent component and an opaque component are bonded bymulti-component injection molding to form a polymer workpiece,

b) the opaque component is irradiated through the transparent componentwith at least one laser and a mark is thereby introduced into the opaquecomponent.

The opaque component contains a colorant. The mark is a localbrightening of the opaque component.

The dimensions of the polymer workpiece can vary widely and thus beideally adapted to the requirements of the individual case. The area ofthe polymer workpiece can, for example, be from 1 cm² to 3 m².Preferably, the polymer workpiece has an area from 100 cm² to 2.5 m², asis customary for panes of motor vehicles and in the construction andarchitectural sector.

The polymer workpiece comprises, according to the invention, at least atransparent component and an opaque component, wherein the opaquecomponent is arranged at least on one region of the transparentcomponent. The polymer workpiece is preferably produced bymulti-component injection molding, wherein, first, the transparentcomponent is injection molded and, then, the opaque component is appliedto at least a region of the transparent component. Of course, inprinciple, the opaque component can be injection molded first, followedby the transparent component. The polymer workpiece is, for example, amotor vehicle pane that contains a transparent polymer component,wherein an opaque polymer component is arranged circumferentially in theedge region on the transparent polymer component. The width of theopaque component is, for example, from 1 cm to 10 cm. The opaquecomponent thus forms a frame.

The polymer workpiece is preferably flat or slightly or highly curved inone or a plurality of spatial directions.

The transparent component of the polymer workpiece preferably containsat least polyethylene (PE), polycarbonates (PC), polypropylene (PP),polystyrene, polybutadiene, polynitriles, polyesters, polyurethanes,polymethyl methacrylates (PMMA), polyacrylates, polyesters, polyamides,polyethylene terephthalate, acrylonitrile butadiene styrene (ABS),styrene acrylonitrile (SAN), acrylonitrile styrene acrylester (ASA),acrylonitrile butadiene styrene-polycarbonate (ABS/PC), and/orcopolymers or mixtures thereof.

The transparent component of the polymer workpiece particularlypreferably contains polycarbonates (PC) and/or polymethyl methacrylate(PMMA). This is particularly advantageous with regard to thetransparency, processing, strength, weather resistance, and chemicalresistance of the polymer workpiece.

In the context of the invention, “transparent” means that an observercan see through the component and can recognize objects that are behindthe component as viewed by the observer. The transparent component canbe colorless. The transparent component can also be colored or tinted.The transmission of the transparent component in the visible spectralrange is, for example, greater than or equal to 50% or even greater thanor equal to 70%.

In the context of the invention, “opaque” means that an observer cannotsee through the component. The transmission of the opaque component inthe visible spectral range is thus clearly reduced and is, for example,less than or equal to 20%, less than or equal to 10%, less than or equalto 5%, in particular roughly 0%.

The transparent component preferably has a layer thickness from 1 mm to20 mm, particularly preferably from 3 mm to 10 mm.

The opaque component of the polymer workpiece preferably contains atleast polyethylene (PE), polycarbonates (PC), polypropylene (PP),polystyrene, polybutadiene, polynitriles, polyesters, polyurethanes,polymethyl methacrylates, polyacrylates, polyesters, polyamides,polyethylene terephthalate, acrylonitrile butadiene styrene (ABS),styrene acrylonitrile (SAN), acrylonitrile styrene acrylester (ASA),acrylonitrile butadiene styrene-polycarbonate (ABS/PC), and/orcopolymers or mixtures thereof, particularly preferably polycarbonates(PC), polyethylene terephthalate (PET), and/or polymethyl methacrylate(PMMA).

The opaque component of the polymer workpiece further contains at leastone colorant. The opacity of the component is obtained by means of thecolorant. The colorant can contain inorganic and/or organic dyes and/orpigments. The colorant can be colourful or not colourful. Suitablecolorants are known to the person skilled in the art and can, forexample, be looked up in the Colour Index of the British Society ofDyers and Colourists and the American Association of Textile Chemistsand Colorists. Preferably, a black pigment is used as the colorant, forexample, carbon black, aniline black, bone black, iron oxide black,spinel black, and/or graphite. Thus, a black opaque component isobtained.

The opaque component preferably has a layer thickness from 0.5 mm to 10mm, particularly preferably from 1 mm to 7 mm.

The mark is applied according to the invention by a laser. The beam ofthe laser enters the polymer workpiece via the surface of thetransparent component facing away from the opaque component. The beam ofthe laser is focused in an advantageous embodiment by an opticalelement, for example, a lens or an objective, on the boundary surfacebetween the transparent component and the opaque component. The focallength of the focusing optical element is preferably from 10 mm to 300mm. Particularly good results are thus obtained. A smaller focal lengthof the optical element requires too short a distance between the polymerworkpiece and the optical element during the marking operation. A largerfocal length results in too great an expansion of the laser focus, bymeans of which the resolution of the marking process and the powerdensity in the focus are limited.

The beam of the laser can be guided between laser and the focusingoptical element by at least one optical waveguide, for example, a glassfiber. Other optical elements can also be arranged in the beam path ofthe laser.

In an advantageous embodiment, the mark is introduced by a movement ofthe beam of the laser into the surface of the opaque component facingthe transparent component. It has been demonstrated that the beam of thelaser results in a brightening of the opaque component in the region ofthe boundary surface between the transparent component and the opaquecomponent. The brightening is clearly discernible through thetransparent component as a mark. The mark preferably appears as at leasta uniformly bright region on the opaque component.

For the laser marking of the polymer workpiece according to theinvention, it is, of course, necessary for the transparent component topermit passage of laser light, i.e., for at least part of the beam ofthe laser to be transmitted through the transparent component. Thefraction of the beam of the laser transmitted through the transparentcomponent is, for example, greater than or equal to 50%, preferablygreater than or equal to 70%, particularly preferably greater than orequal to 80%, and most particularly preferably than or equal to 90%.

The mark can have any configuration, for example, a two-dimensionalgeometric figure, a pictogram, a company or trademark symbol, aninscription in the form of letters and/or numbers, or combinationsthereof. By means of the marking, the polymer workpiece can be providedwith a manufacturers code, an approval mark, a production date, oroptical effects.

The movement of the beam of the laser is preferably done by at least onemirror that is connected to a movable part. By means of the movablepart, the mirror can be adjusted in two directions, preferably twodirections orthogonal to each other, particularly preferablyhorizontally and vertically. The movement of the beam of the laser canalso be done by a plurality of mirrors connected in each case to amovable part. For example, the movement of the beam of the laser can bedone by two mirrors, where one mirror can be adjusted horizontally andthe other mirror vertically. During laser marking, the polymer workpieceis preferably fixed in a part holder.

Alternatively, the beam of the laser can be stationary and the polymerworkpiece can be moved during the marking operation.

The beam of the laser is preferably moved at a speed of 200 mm/s to 5000mm/s over the boundary surface between the transparent component and theopaque component. Particularly good results are thus obtained.

A solid-state laser, for example, an Nd:YAG laser, an Nd:Cr:YAG laser,an Nd:Ce:YAG laser or a Yb:YAG laser, is preferably used as the laser.Particularly preferably, a fiber laser is used with, for example, aytterbium-doped glass fiber as the active medium. This is particularlyadvantageous with regard to the beam quality of the laser beam. Theemission wavelength of the laser is preferably from 600 nm to 3000 nm,particularly preferably from 900 nm to 1500 nm, for example, roughly1064 nm. Particularly good results are thus obtained.

However, a different type of laser can also be used according to theinvention, for example, a gas laser, such as a CO₂ laser.

The laser can be used in continuous wave operation. Preferably, thelaser is operated in pulsed mode. This is particularly advantageous withregard to high power density in the polymer substrate. The pulsefrequency is preferably from 1 kHz to 500 kHz, particularly preferablyfrom 20 kHz to 150 kHz, the pulse duration is preferably from 5 ns to300 ns, particularly preferably from 50 ns to 150 ns. This isparticularly advantageous with regard to the power density of the laserduring the laser marking.

The output power of the beam of the laser is preferably from 1 W to 50W, particularly preferably from 15 W to 35 W. This is particularlyadvantageous regard to an efficient marking of the polymer substrate.

In an advantageous embodiment of the invention, a protective coating isapplied to the polymer workpiece. Preferably, thermal curing or UVcuring coating systems based on polysiloxanes, polyacrylates,polymethacrylates, and/or polyurethanes are used. The protective coatingpreferably has a layer thickness from 1 μm to 50 μm, particularlypreferably from 2 μm to 25 μm. The particular advantage resides inscratch resistance and weather resistance as well as chemical resistanceof the polymer workpiece due to the protective coating.

The protective coating can also contain coloring compounds and pigments,UV blockers, preservatives, as well as components for increasing scratchresistance, for example, nanoparticles.

The protective coating can, for example, be applied to the polymerworkpiece by a dipping, flooding, or spraying method. The protectivecoating is cured after application preferably by temperature and/or UVlight. In the case of production of the polymer workpiece by injectionmolding, the protective coating can also be applied by an in-moldcoating method.

Suitable protective coating products are, for example, AS4000, AS4700,variants of PHC587 or UVHC300, which are produced by the companyMomentive.

The protective coating can also comprise a plurality of layers,preferably an adhesion promoting layer on the polymer workpiece and alacquer coating on the adhesion promoting layer. The adhesion promotinglayer can contain, for example, acrylates and have a layer thicknessfrom 0.4 μm to 5 μm. The lacquer coating can contain, for example,polysiloxanes and have a layer thickness from 1 μm to 15 μm. Theadhesion promoting layer is preferably dried after application, beforethe lacquer coating is applied.

The protective coating is preferably applied after the laser marking ofthe polymer workpiece according to the invention. The mark is arrangedin the interior of the polymer workpiece such that during theapplication of the protective coating after the laser marking, nocoating distribution problems or other disadvantageous impairments ofthe protective coating and/or the mark occur.

The laser-marked polymer workpiece is preferably used as a pane or partof a pane of means of transportation for travel on land, in the air, oron water, in particular as a rear window pane, windshield, side pane,and/or roof pane of motor vehicles. The laser-marked polymer workpiececan be used as a window pane, but also as an interior part, for example,as a switch or sensing device.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The invention is explained in detail with reference to drawings andexemplary embodiments. The drawings are schematic representations andnot true to scale. The drawings in no way restrict the invention. Theydepict:

FIG. 1 a top plan view of one embodiment of the laser-marked polymerworkpiece according to the invention,

FIG. 2 a cross-section along A-A′ through the laser-marked polymerworkpiece according to the invention of FIG. 1,

FIG. 2a an enlarged view of the detail Z of FIG. 2,

FIG. 3 a cross-section along A-A′ through the polymer workpieceaccording to the invention of FIG. 1 during the laser marking,

FIG. 4 a detailed flow chart of the method according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 and FIG. 2 each depict a detail of the polymer workpiece 1according to the invention. It is a side window pane of a passenger carand has a height of 30 cm and a width of 28 cm. The polymer workpiece 1contains a transparent component 2. An opaque component 3 with a widthof 4 cm is arranged circumferentially on the transparent component 2 inthe edge region of the polymer workpiece 1. FIG. 1 depicts the top planview of the surface of the transparent component 2 turned away from theopaque component 3. The opaque component 3 can be discerned in the topplan view through the transparent component 2. The polymer workpiece 1was produced by multi-component injection molding. The transparentcomponent 2 has a thickness of 4 mm and contains polycarbonate (PC). Theopaque component 3 has a thickness of 2 mm. The opaque component 3contains a mineral-filled polycarbonate (PC)-polyethylene terephthalate(PET) mixture. The starting material for the injection molding of theopaque component 3 was prepared by the company Teijin Chemicals Ltd.(Panlite Y-0346 Color No. TG6654). The polymer workpiece 1 is nottransparent in the region of the opaque component 3. The side windowpane can thus be connected, for example, glued, to the vehicle body in amanner not visible to the observer, with the opaque component 3preferably arranged facing the interior of the vehicle.

A mark 4 is arranged in at least one region of the opaque component 3.The mark 4 is introduced according to the invention into the opaquecomponent 3 on the boundary surface between the transparent component 2and the opaque component 3. The mark 4 is realized as a brightenedregion on the surface of the opaque component 3. The mark 4 is depictedfor the sake of simplicity as a filled-in circle. In practice, the mark4 can be, for example, a manufacturers symbol, a trademark symbol, amanufacturers code, a production date, and/or an approval mark.

By means of the arrangement according to the invention of the mark 4 inthe interior of the polymer workpiece 1 on the boundary surface betweenthe transparent component 2 and the opaque component 3, the mark 4 isadvantageously protected against environmental influences, such asmechanical damage, for example. In addition, the mark 4 does not resultin coating distribution problems, with the application of a coating (notshown) of the polymer workpiece 1, for example, a protective lacquercoating, after laser marking.

FIG. 2a depicts an enlarged view of the detail Z identified by a circlein FIG. 2. A region of the transparent component 2, a region of theopaque component 3 as well as the mark 4 introduced into the surface ofthe opaque component 3 facing the transparent component 2 can be seen.

FIG. 3 depicts a cross-section A-A′ through the polymer workpiece ofFIG. 1 during the laser marking according to the invention. The beam ofthe laser 5 enters the polymer workpiece 1 via the surface of thetransparent component 2 facing away from the opaque component 3. Thebeam of a laser 5 is focused by means of a lens 6 on the boundarysurface or interface between the transparent component 2 and the opaquecomponent 3 of the polymer workpiece 1. The focal length of the lens 6is 160 mm. The laser 5 is a diode-pumped fiber laser with a 2-m-longytterbium-doped glass fiber as the active medium. The emissionwavelength of the laser 5 is about 1063 nm. The laser 5 is operated inpulsed mode with a pulse duration of 110 ns and a pulse frequency of 60kHz. A mirror 7 is arranged in the beam path of the laser 5. By movingthe mirror 7, the focus of the beam of the laser 5 can be moved over theboundary surface between the transparent component 2 and the opaquecomponent 3 of the polymer workpiece 1.

The beam of the laser 5 results, already after an exposure time in therange of a few milliseconds, in a clear brightening on the surface ofthe opaque component 3. By means of the movement of the focused beam ofthe laser 5 over the boundary surface between the transparent component2 and the opaque component 3 of the polymer workpiece 1, a mark 4, forexample, a manufacturers symbol, a manufacturers code, a productiondate, or an approval mark, can thus be permanently applied.

FIG. 4 depicts, by way of example, the method according to the inventionfor producing a laser-marked polymer workpiece 1.

Test specimens of laser-marked polymer workpieces 1 according to theinvention according to FIG. 1 were made with the method according to theinvention. The laser marking was performed with the laser marking systemDP20F of the company FOBA, comprising a laser 5, a mirror 7 and a lens6. The mark 4 comprised letters, numbers, and geometric figures. Withall test specimens, the mark 4 was clearly recognizable. The minimumline width of the mark 4 was roughly 0.1 mm.

It was unexpected and surprising for the person skilled in the art thata mark 4 of a polymer workpiece 1 can be provided in a simple andreliable manner without altering the surface of the polymer workpiece 1.

LIST OF REFERENCE CHARACTERS

-   -   (1) polymer workpiece    -   (2) transparent component    -   (3) opaque component    -   (4) mark    -   (5) laser    -   (6) lens    -   (7) adjustable mirror    -   A-A′ section line    -   Z detail of the polymer workpiece 1

What is claimed is:
 1. A laser-marked polymer workpiece, comprising: atransparent component having a transmission in visible spectral rangeequal to or greater than 50%; an opaque component having a transmissionin the visible spectral range equal to or less than 20%, the opaquecomponent containing at least one colorant and being applied to at leastone region of the transparent component, the opaque component comprisinga surface facing the transparent component; and a laser mark on thesurface of the opaque component, the laser mark being a brightening ofthe opaque component, wherein the opaque component is devoid of a lasersensitive additive, and wherein the at least one colorant comprises atleast one black pigment.
 2. The workpiece according to claim 1, whereina thickness of the transparent component is from 1 mm to 20 mm.
 3. Theworkpiece according to claim 1, wherein a thickness of the opaquecomponent is from 0.5 mm to 10 mm.
 4. The workpiece according to claim1, wherein the workpiece comprises one or more of polycarbonate,polyethylene terephthalate, or polymethyl methacrylate.
 5. The workpieceaccording to claim 1, wherein the black pigment comprises one or more ofcarbon black, aniline black, bone black, iron oxide black, spinel black,or graphite.
 6. The workpiece according to claim 1, wherein the opaquecomponent is arranged on the transparent component circumferentially inan edge region of the polymer workpiece having a width from 1 cm to 10cm.
 7. The workpiece according to claim 1, wherein the laser markcomprises at least a letter, a number, a geometric figure, a symbol,and/or a pictogram.
 8. The workpiece according to claim 1, wherein thelaser mark appears as at least one uniformly bright region on the opaquecomponent.
 9. The workpiece according to claim 1, further comprising aprotective coating, wherein the protective coating comprises one or moreof a polysiloxane, a polyacrylate, a polymethacrylate, or apolyurethane.
 10. The workpiece according to claim 9, wherein theprotective coating has a thickness from 1 μm to 50 μm.
 11. The workpieceaccording to claim 10, wherein the protective coating has a thicknessfrom 2 μm to 25 μm.
 12. The workpiece according to claim 1, wherein athickness of the transparent component is from 3 mm to 10 mm.
 13. Theworkpiece according to claim 1, wherein a thickness of the opaquecomponent is from 1 mm to 7 mm.
 14. A method, comprising: using alaser-marked polymer workpiece as a pane or as a part of a pane of meansof transportation for travel on land, in the air, or on water, inparticular as a windshield, rear window, side window, and/or roof paneof motor vehicles, wherein the laser-marked polymer workpiece includes atransparent component having a transmission in visible spectral rangeequal to or greater than 50%, an opaque component having a transmissionin the visible spectral range equal to or less than 20%, the opaquecomponent containing at least one colorant and being applied to at leastone region of the transparent component the opaque component comprisinga surface facing the transparent component; and a laser mark on thesurface of the opaque component, the mark being a brightening of theopaque component, wherein the opaque component is devoid of a lasersensitive additive, and wherein the at least one colorant comprises atleast one black pigment.